This invention relates to printing machines and more particularly to an abnormal-paper sensing apparatus in the printing machine which senses a folded corner of a sheet of printing paper which hits against front stays provided at a front end of an insertion guide plate and stops thereat in response to the disappearance of reflected light from the folded corner of the sheet of paper.
In a sheet-fed printing machine, sheets of printing paper stacked on a stacker of a paper feeder are drawn and fed one by one by a sucker, starting with the top sheet, to a feeder board and then delivered onto an insertion guide plate with the aid of a carrier tape and feed rolls. The sheet of paper then hits against front stays provided at a front end of the insertion guide plate and stops thereat with it being adjusted with reference to the vertical by the front stays and also with respect to right and left by a transverse needle device. The sheet of paper which has hit against and stopped is then captured and carried by a pawl of a swing device and then is printed while it is being carried with it being captured by a thicker pawl.
Sheets of paper are required to be fed one by one to the printing machine without being bent or folded. Therefore, when undesirable feeding such as feeding of a sheet of paper having a folded corner of double-sheet feeding has occurred, this is sensed and capture by the pawls and paper-feeding onto the insertion guide plate are stopped. An abnormal sheet of paper of this type is folded at its front right and/or left corner into a triangle. In order to sense this corner folding, reflection type sensors are conventionally provided several millimeters before the front stays above the sheet of paper to sense the presence of reflected light from the sheet of paper which hits against the front stays and stops to thereby determine that there is corner folding in the sheet due to the fact that no reflected light is received. When a sheet of paper having a different size is used, the sensor is moved correspondingly.
In such corner folding sensor, however, the insertion guide plate itself will reflect light which is projected to its exposed portions. Therefore, the sensor is likely to erroneously determine that there is no corner folding although there is actually corner folding, and thereby continue paper feeding. In order to avoid this, through holes are provided in the insertion guide plate so as to cause the projected light to pass through the hole without reflecting the projected light when there is corresponding corner folding. However, in order to cope with a different paper size or alter the sensing position, the holes must be elongated in the form of slots, so that a sheet of paper sliding on the insertion guide plate may be hooked at its corner into the elongated slot and bent to thereby operate the sensor, thus stopping feeding of the sheet of paper. Provision of such an elongated hole would weaken the strength of the end portion of the insertion guide plate.